1. Field of the Invention
This invention relates to an image reading device provided with a reading carriage which is placed at a prescribed fixing position so as to read a document transferred by a document transferring device.
2. Description of the Prior Art
An image reading device used for an image forming device such as a copying machine and facsimile apparatus has a document reading surface opposed to an image reading glass. A carriage of an image reading portion (hereinafter, simply referred to as an "image reading portion") of the image reading device has a function of reading an image on a document while moving from a home position in a sub-scanning direction to subjecting the image of the document to main scanning. In a case that an automatic document feeder (hereinafter, simply referred to as an "ADF") is attached thereto, the document is moved along the reading portion in the sub-scanning direction at a constant speed. Therefore, the aforesaid reading portion is retained at the prescribed standby position and serves to scan the documents fed from the ADF in succession in the main scanning direction so as to read images on the documents. Upon reading the images on the documents, the documents are discharged through a document discharge port.
However, in a case that the document has images on its both surfaces, the obverse and reverse surfaces (the image surface which is first read is called "obverse", and the image surface surface which is secondly read is called "reverse" in the description including the appended claims) should be moved over the image reading position in succession. Accordingly, the image on the obverse surface is first read by moving the document from its one end in the forward direction in such a state that the obverse surface is opposed to the image reading position, and thereafter, the document is turned upside down to read the image on the reverse surface. That is, the turned document is moved over the aforementioned image reading position with its reverse surface opposed to the image reading position. Thus, upon reading the images on the both surfaces of the document, the document is sent out through the document discharge port.
Conventional document transferring mechanisms for use in the document reading device for reading the document having the images on its both surfaces have been disclosed in Japanese Patent Application Public Disclosures HEI 02-63262(A), 06-247642(A) and 08-133551(A).
FIGS. 16(a)-16(d) show a first example of the prior art devices as noted above. In this device, a document sent from a document entrance side on the right side of the drawing is moved from its one end in the forward direction through an image reading position at which a reading portion is placed under a reading feed roller (in the direction from the right side to the left side of the drawing) in such a state that one image surface to be first read faces downward. Consequently, the image on the obverse surface of the document is read by the reading portion FIG. 16(a). Next, after the other end of the document passes through the reading position to complete the reading of the image on the obverse surface, the document stops for a while at the document discharge portion shown on the left side of the drawing FIG. 16(b). Thereafter, the document moves from its other end and goes around the reading feed roller in the clockwise direction so as to pass through the reading position with the reverse surface facing the reading portion. Consequently, the image on the reverse surface of the document is read FIG. 16(c). Then, the document is sent out in the document discharging direction toward the left side of the drawing FIG. 16(D).
FIGS. 17(a)-17(d) show a second example of the prior art devices as noted above. In this conventional device, a document fed from the document entrance side on the right side of the drawing is moved from its one end in the forward direction through a reading position at which a reading portion is placed under a reading feed roller in such a state that one image surface to be first read faces downward in the same manner as the first example described above FIG. 17(a). Consequently, the image on the obverse surface of the document is read by the reading portion. After reading the image on the obverse surface of the document, the document is moved from its one end toward the document discharge side on the left side of the drawing in the clockwise direction (may be moved even in the counterclockwise direction) so as to be turned upside down FIG. 17(b). The turned document is next moved over the reading position in the reverse direction (from the left side to the right side of the drawing) with its reverse surface facing the reading portion, so that the image on the reverse surface is read FIG. 17(c). Then, the document is moved around the reading feed roller in the counterclockwise direction while reading the image on the reverse surface of the document and sent out in the document discharging direction FIG. 17(d).
However, in the first example of the conventional devices, the directions in which the images of the obverse and reverse surfaces of the document are read are opposite to each other. Namely, the obverse surface of the document to be first read is scanned from the leading end of the document, but the reverse surface to be read later is scanned from the tail end of the document. Thus, this conventional device entails problem such as difficulty in bringing the images, which are read from the obverse and reverse surfaces of the document and should be reproduced on a sheet of paper, into perfect coincidence on the both sides of the sheet.
On the other hand, the second example of the conventional devices is free from the disadvantage brought about by the first example, because the images on the obverse and reverse surfaces are read in the same direction in the second example. However, after reading the image on the obverse surface of the document, the document must be moved from its leading end to be turned upside down on the document discharge side on the left side of the drawing. Besides, even a document of any size is required to prevent its leading and tail ends from overlapping with each other at the reading position when turning on the document discharge side. Therefore, this conventional device calls for a large space for turning the document upside down on the document discharge side, resulting in a large overall size of the ADF device.